This invention relates generally to heat sealing or bonding of plastic sheets; more particularly, it concerns the production of uniformly satisfactory, high frequency bonding of the sheets along seams of substantial length.
When multiple plastic sheets are heat bonded as by high frequency techniques, certain problems are encountered. For example, irregular bonding may occur due to improper energy distribution resulting from energy feed lines of unequal lengths. Unsatisfactory bonding may also result from unequal gaps across which the energy flows between metallic surfaces defining a zone receiving the plastic layers or sheets to be bonded. These problems are enhanced and made extremely difficult to overcome where the seams to be bonded are of relatively great lengths, and where a movable platen is employed to close against and retract from the plastic sheets, as is required for high production rates. So far as I am aware, there has been no solution to these problems which embodies the unusually advantageous method, features of construction, mode of operation and results as now are afforded by the present invention.